Want to do something with space or nuclear fusion

I'm currently going into my second year of psychology, and I was thinking about picking up the first year physics and calculus courses to take a double major in psych and physics. Anyways, my end goal will likely have something to do with space or nuclear fusion (admittedly, scifi movies sometimes get me thinking "I would love to do that").

My question: after graduating with a B.Sc. in psych and physics, are there any graduate level programs in aerospace/space physics or engineering that I would be able to take, or would I be best to go on with a masters in nuclear engineering?